1. Field of the Invention
The present invention relates to Digital Subscriber Line (DSL) methods and systems.
2. Description of the Related Art
DSL is a well known technology for providing high-speed access to the Internet. Each premise of a DSL subscriber is equipped with a DSL modem. The DSL modem communicates via existing telephone lines with a DSL Access Multiplexer (DSLAM) located at a telephone company office such as a central office. The DSLAM may serve hundreds of DSL subscribers located in a servicing area. The DSLAM aggregates traffic received from various DSL subscribers to send to a network center via a fiber optic link. The network center, in turn, provides access to a packet data core network, which provides access to the Internet.
Some DSL subscribers are served by digital loop carriers (DLCs). DLCs are located remotely from a central office to serve subscribers who have no direct connection to the central office.
A Media Access Control (MAC) layer is a layer of a distributed communications system concerned with the control of access to a medium that is shared between two or more entities. In DSL applications, the MAC layer comprises an Asynchronous Transfer Mode (ATM) layer between the DSL modem and the DSLAM or DLC, and an ATM layer between the DSLAM or DLC and the network center which provides the packet data core network.
A measure of service quality provided to a subscriber is known as Quality of Service (QoS). For ATM connections, the QoS can be measured by parameters such as Cell Error Ratio, Severely Errored Cell Block Ratio, Cell Loss Ration, Cell Misinsertion Rate, Cell Transfer Delay, Mean Cell Transfer Delay and Cell Delay Variability. Since DSL access networks use ATM layers, the QoS for DSL is defined with respect to ATM.